Silent Mating Type Information Regulation Research Articles

Dual role of Zn2+ in maintaining structural integrity and suppressing deacetylase activity of SIRT1

Zn(2+) directly participates in catalysis of histone deacetylase (HDAC) Classes I, II, IV enzymes while its role in HDAC Class III activity is not well established. Herein we investigated the effects of Zn(2+) on the deacetylase activity of sirtuin 1 (silent mating type information regulation 2 homolog 1, SIRT1). We found that the inherent Zn(2+) at the zinc-finger motif of SIRT1 is essential for the structural integrity and the deacetylase activity of SIRT1, whereas the exogenous Zn(2+) strongly inhibits the deacetylase activity with an IC(50) of 0.82muM for Zn(Gly)(2). SIRT1 activity suppressed by the exogenous Zn(2+) can be fully recovered by the metal chelator EDTA but not by the activator resveratrol. We also identified Zn(2+) as a noncompetitive inhibitor for the substrates of NAD(+) and the acetyl peptide P53-AMC. The 8-anilino-1-naphthalenesulfonic acid (ANS) fluorescence titration experiments and site-directed mutagenesis study suggested that the exogenous Zn(2+) binds to SIRT1 but not at the zinc-finger motif. These results indicate that Zn(2+) plays a dual role in SIRT1 activity. Inherent Zn(2+) at the zinc-finger motif is structurally related and essential for SIRT1 activity. On the other hand, Zn(2+) may also bind to another site different from the zinc-finger motif or the binding sites for the substrates or resveratrol and act as a potent inhibitor of SIRT1.

RelA/p65 functions to maintain cellular senescence by regulating genomic stability and DNA repair

Nuclear factor (NF)-kappaB is a positive regulator of tumour development and progression, but how it functions in normal cells leading to oncogenesis is not clear. As cellular senescence has proven to be an intrinsic tumour suppressor mechanism that cells must overcome to establish deregulated growth, we used primary fibroblasts to follow NF-kappaB function in cells transitioning from senescence to subsequent immortalization. Our findings show that RelA/p65(-/-) murine fibroblasts immortalize at considerably faster rates than RelA/p65(+/+) cells. The ability of RelA/p65(-/-) fibroblasts to escape senescence earlier is due to their genomic instability, characterized by high frequencies of DNA mutations, gene deletions and gross chromosomal translocations. This increase in genomic instability is closely related to a compromised DNA repair that occurs in both murine RelA/p65(-/-) fibroblasts and tissues. Significantly, these results can also be duplicated in human fibroblasts lacking NF-kappaB. Altogether, our findings present a fresh perspective on the role of NF-kappaB as a tumour suppressor, which acts in pre-neoplastic cells to maintain cellular senescence by promoting DNA repair and genomic stability.

3D-QSAR of SIRT1 Activators Targeting Against Diet-Induced Metabolic Syndrome

The prevalence of metabolic syndrome associated with increased risk for cardiovascular disease, type 2 diabetes, or cancer has been increasing over the past decade. While traditional drug discovery efforts have been tackling these diseases by aiming at individual targets, recent studies in humans have suggested the possibility that the collection of the metabolic degenerative processes can be approached as a whole by controlling diet, especially calorie restriction. Studies of calorie restriction in a broad range of animals including primates, mice, worms, and yeast have suggested that a reduction in calorie intake lengthens lifespan and protects against cancer and other age-related diseases. There has therefore been much interest in developing pharmacological agents that mimic the effects of calorie restriction. Resveratrol, a natural product derived from grapes, is the first reported mimetic of calorie restriction. Ever since the mode of action of resveratrol was elucidated to activate SIRT1 [sirtuin (silent mating type information regulation 2 homolog) 1] which, in turn, deacetylates p53 and promotes cell survival in a NAD-dependent manner, numerous efforts have been devoted to discover novel activators of SIRT1. Through high throughput screening of a large selection of small molecules, Milne et al. identified three imidazothiazole derivatives as potent SIRT1 activators, which are structurally unrelated to but 1,000-fold more active than resveratrol. Recently, in order to improve the potency as well as the solubility of the imidazothiazole derivatives, two different libraries of analogues, imidazo[1,2-b]thiazole and oxazolo[4,5-b]pyridine, were constructed and extensively investigated. The aim of the present study is to derive a predictive method for designing novel potent SIRT1 activators through construction of 3D QSAR models. For this purpose, from the literature, SIRT1 activation data of 33 imidazothiazole and oxazolopyridine derivatives were obtained (Fig. 1). At first, the 33 compounds were divided into two groups: 27 compounds as a training set and the other 6 compounds as a test set. The CoMFA (comparative molecular force analysis) and CoMSIA (comparative molecular similarity indices analysis) methods were employed for deriving 3D-QSAR models consisting for a training set of 27 imidazothiazole and oxazolopyridine derivatives, keeping in vitro activity as a dependent variable. The 3D-QSAR models were then validated using a test set of 6 compounds, which were not included in the development of the models. Finally, the contour plots of the 3D-QSAR model were analyzed to

SIRT1 markedly extends replicative lifespan if the NAD + salvage pathway is enhanced

Sir2 mediates lifespan extension in lower eukaryotes but whether its mammalian homolog, sirtuin 1, silent mating type information regulation 2 homolog (SIRT1), is a longevity protein is controversial. We stably introduced the SIRT1 gene into human vascular smooth muscle cells (SMCs) and observed minimal extension of replicative lifespan. However, SIRT1 activity was found to be exquisitely dependent on nicotinamide phosphoribosyltransferase (Nampt) activity. Moreover, overexpression of Nampt converted SIRT1-overexpressing SMCs to senescence-resistant cells together with heightened SIRT1 activity, suppressed p21, and strikingly lengthened replicative lifespan. Thus, SIRT1 can markedly postpone SMC senescence, but this requires overcoming an otherwise vulnerable nicotinamide adenine dinucleotide salvage reaction in aging SMCs.

Expression of DBC1 and SIRT1 Is Associated with Poor Prognosis of Gastric Carcinoma

SIRT1 (silent mating-type information regulation 2 homologue 1) expression has been reported to predict poor survival in some cancers. We therefore investigated the expression levels of SIRT1 and its negative regulator, DBC1 (deleted in breast cancer 1), in gastric cancer patients. We evaluated immunohistochemical expression of DBC1, SIRT1, and p53 using 3-mm tumor cores from 177 gastric cancer patients for tissue microarray. Positive expressions of DBC1 and SIRT1 were seen in 62% (109 of 177) and in 73% (130 of 177) of patients, respectively. Expression of DBC1 was significantly correlated with tumor stage (P = 0.007), lymph node metastasis (P < 0.001), tumor invasion (P = 0.001), venous invasion (P = 0.001), histologic types (P < 0.001), p53 expression (P < 0.001), and SIRT1 expression (P < 0.001). SIRT1 expression was also significantly correlated with tumor stage (P < 0.001), lymph node metastasis (P < 0.001), tumor invasion (P < 0.001), histologic types (P < 0.001), and p53 expression (P = 0.001). In addition, expression of DBC1 was significantly associated with shorter overall survival and relapse-free survival by univariate analysis (P < 0.001 and P < 0.001, respectively). SIRT1 expression was also significantly associated with shorter overall survival and relapse-free survival by univariate analysis (P = 0.001 and P = 0.001, respectively). Multivariate analysis showed that tumor stage and expression of DBC1 were independent prognostic factors significantly associated with overall survival and relapse-free survival. This study shows that expression of DBC1 and SIRT1 is a significant prognostic indicator for gastric carcinoma patients.

DNA pooling: a comprehensive, multi‐stage association analysis of ACSL6 and SIRT5 polymorphisms in schizophrenia

Many candidate gene association studies have evaluated incomplete, unrepresentative sets of single nucleotide polymorphisms (SNPs), producing non-significant results that are difficult to interpret. Using a rapid, efficient strategy designed to investigate all common SNPs, we tested associations between schizophrenia and two positional candidate genes: ACSL6 (Acyl-Coenzyme A synthetase long-chain family member 6) and SIRT5 (silent mating type information regulation 2 homologue 5). We initially evaluated the utility of DNA sequencing traces to estimate SNP allele frequencies in pooled DNA samples. The mean variances for the DNA sequencing estimates were acceptable and were comparable to other published methods (mean variance: 0.0008, range 0-0.0119). Using pooled DNA samples from cases with schizophrenia/schizoaffective disorder (Diagnostic and Statistical Manual of Mental Disorders edition IV criteria) and controls (n=200, each group), we next sequenced all exons, introns and flanking upstream/downstream sequences for ACSL6 and SIRT5. Among 69 identified SNPs, case-control allele frequency comparisons revealed nine suggestive associations (P<0.2). Each of these SNPs was next genotyped in the individual samples composing the pools. A suggestive association with rs 11743803 at ACSL6 remained (allele-wise P=0.02), with diminished evidence in an extended sample (448 cases, 554 controls, P=0.062). In conclusion, we propose a multi-stage method for comprehensive, rapid, efficient and economical genetic association analysis that enables simultaneous SNP detection and allele frequency estimation in large samples. This strategy may be particularly useful for research groups lacking access to high throughput genotyping facilities. Our analyses did not yield convincing evidence for associations of schizophrenia with ACSL6 or SIRT5.

Microarray analysis of differentially expressed genes in mouse bone marrow tissues after ionizing radiation

Purpose: To identify differentially expressed genes in mouse bone marrow involved in radiation-induced injury.Materials and methods: Microarray analysis was used to identify the differentially expressed genes and other techniques, e.g., polymerase chain reaction (PCR), western-blotting and antisense were also used to validate the results.Results: DNA microarray analysis demonstrated that the mRNA of 34 genes increased and 69 genes decreased in mouse bone marrow cells (BMC) from C57BL mice 6h after a whole body dose of 6.5 Gy. These differentially expressed genes were involved in a number of processes including DNA replication/repair, proliferation/apoptosis, cell cycle control and RNA processing. In these experiments, a decline of the mammalian homolog Sir2a (an acronym for the silent mating type information regulation 2 homolog [SIRT1]) mRNA accompanied by an increase of P53 protein acetylation was observed in irradiated BMC. To determine whether the reduced SIRT1 is related to the higher acetylation status of P53 after irradiation, we designed and synthesized antisense oligonucleotides (AS) targeting human SIRT1 mRNA. Notably, AS transfection increased tumor protein 53 (P53) protein acetylation and bax-luciferase activity in human bone marrow stromal cell line (HS-5) after radiation. Furthermore, the AS transfer stimulated cell apoptosis in post-irradiation HS-5 cells.Conclusion: Ionizing radiation (IR) affects the expression of a series of genes including genes involved in G1/S transition and the P53 pathway. Among those, reduction of SIRT1 was seen to be involved in transactivation of P53.